Identify themselves as LE, and of course physically represent as such, unambiguously, then demand the person put down the firearm. "Active Shooter" has no meaning just because the word is used. Also consider what everyone long forgot and few pay attention to; officers are paid, not volunteers. Risk is part of the job. You cannot shoot everything you think might be a threat. One can also question the quality of the system that handles emergency calls, or that responds to them. There are lots of guns in America. And lots of people who can say the words "active shooter". And often enough, phones and other objects are conveniently interpreted as guns, so I am not convinced that is the most important variable. Did he point it at the officers? If so, were the officers in proper uniform?

Now, if I were to answer your question, I would say it first depends on circumstances. I have encountered many people with guns. But if I was and active officer and encountered someone with a gun, I would do my best so that the encounter was arranged in a manner that gave me some advantage and at least a second or two to think before acting. Sometimes, mistakes are made though, and they always will be made. But the fact someone had a gun is no excuse.